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In India, an air-powered car

By Sarah Korones | May 13, 2012, 6:07 PM PDT

Forget electricity, cars of the future could run on air.

India-based Tata Motors claims that it has successfully demonstrated a compressed air engine and is now looking to develop a market-ready product. The concept for the air-powered car is not a new one, but Tata, which holds the license for Motor Development International’s (MDI) air engine technologies, may be the first firm to bring the idea to fruition.

The pneumatic motor, or compressed air engine, is similar in many ways to the internal combustion engine. Both varieties use pistons to turn a crankshaft and subsequently power the vehicle. While the internal combustion engine uses fuel to force the pistons to move, the pneumatic motor uses air.

There are a quite a few limitations to the air-powered car, however. As Jesse Emspak of Discovery News points out, compressed air engines can only power a car at speeds of about 30 to 35 miles per hour, meaning they would need to be powered by an onboard electric or gas air compressor.

Another issue is range and the amount of air that can be stored in a single tank. The tanks themselves would need to be extremely strong and filling them could take hours at a time.

While Tata has not announced the details of its compressed air engine, it seems likely that the company has tackled at least some of these issues in order to make a marketable product.

[via Discovery News via Gizmag]

Image: MDI

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About Sarah Korones

Sarah Korones was a contributing editor for SmartPlanet from 2012 to 2013.

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Never a free lunch, but it's an energy capacity trade-off.

There are 2 big issues in transportation energy storage technologies are energy-to-weight capacity and energy-to-volume capacity.

Gasoline has a 8.6kWh/L and 45MJ/kg, thus meaning it gives a big bang for a small mass and a small volume.

Hydrogen by comparison has 120MJ/kg but 0.53kWh/L @ 20MPA. It's that last number which is problem for hydrogen as a fuel. To get it near gasoline, you need to liquefy it and that increases the energy expense to produce it.

Li Ion Batteries have an energy density of 6kWh/L but only between 0.4 and 0.9 MJ/kg. This means they while they can store almost as much energy for a given volume, they weigh considerably more. The two biggest items affecting equivalent gas mileage are weight and drag. So their high weight is a very serious problem.

Compressed air, which is far more variable, generally has a much greater MJ/kg capacity than electric batteries, but in the past, their KWh/L has been much lower. So while they save a lot of weight, for the volume, they don't store as much.

To give you an idea, an electric moped weighs twice what an air-powered moped does (which weighs less than a gas moped). That extra battery weight reduces the range of the electric moped compared to a gas moped. However, the reduced energy capacity of the pneumatic moped reduces its range by usually the same amount. So you end up lighter, but with less energy. Or you end up heavier which uses more energy. So it seems like six of one or half a dozen of the other.

In the one case I saw of the air-powered wheelchair, the reason I saw for it being built was that was that access to electricity was extremely difficult. The village had only a few solar panels and a small wind generator. But the chair's tanks allowed a human with a cheap air pump to recharge them. The chair's lightness also allowed the chair, when the cylinders were depleted, to be more easily pushed over the non-paved terrain. An electric pump was easily light enough to carry for when electricity was available. So given the absence of easily access to abundant electricity, and the ease at which others could, as needed, recharge the chair, or move it if required, pneumatics made sense.

So the trade-offs become important depending on where you're using the technology.

Edited by mheartwood

Updated - 14th May 2012

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In

And where does one get inexpensive LN2?

Might as well use hydrogen. It's even more plentiful.

Posted by JohnMcGrew@...

16th May 2012

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Is this a trend toward retro thinking?

A french company made a prototype air powered car in 2004. They are great city cars.

Their design was inspired by early steam powered cars.

http://www.gizmag.com/go/3523/

You can also refil it right now at most gas stations.

There are a few other prototypes running built on the same companies technology. They even have a long range hybrid.

http://www.mdi.lu/english/produits.php

Posted by Hates Idiots

14th May 2012

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Still not ready for prime time

Since MDI has been unable to bring their early designs to market (despite their claims that they have), they have teamed with Tata -- though it looks like the hurtles that have always stood in the way continue to. It's a great idea - always has been - but the realities of the limitations of the physics of air power have yet to be overcome. Still, I'm glad that there are those who keep trying. Perhaps one day that hidden key will be found.

Posted by justajo

14th May 2012

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There is no free lunch.

And where does the compressed air come from? And if an air compressor must be carried and run to extend range, what's the point over conventional technology?

Posted by JohnMcGrew@...

14th May 2012

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No free lunch, but cute.

The 2004 french prototype used something that has not been adopted by any company.

The test driver used a small solar panel hooked up to one of those little 12 volt emergency compressors to refill the tank on the fly.

It was a hack install, but it worked. The compressor weighed only 2 lbs and was capable of topping off the tank an about 2 hours.

The beauty of the setup was the pneumatic engine shuts down at traffic lights, but pedestrians could hear the little compressor whirring away recharging the tank.

Advantages included being recharged by another cars 12 volt outlet and easy availability to plug in almost anywhere with a small adapter. Both of which are either impossible to do or too time consuming to do with an EV.

Posted by Hates Idiots

Updated - 14th May 2012

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+3 Votes

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Never a free lunch, but it's an energy capacity trade-off.

Posted by mheartwood

Updated - 14th May 2012

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Urban advatages over EVs. Low power and low cost..

The short range, comparable to the Chevy Volt, and low top speed make them a far less costly inner city alternative to EVs.

If you plan on staying in the city they could be very affordable to operate.

The 2004 french prototype was being tested as a cab.

Posted by Hates Idiots

14th May 2012

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Air power

A compressed air tank can replace the chemical battery in a hybrid car. This would avoid the crash/fire hazards of batteries and the complications of electrical control systems. The IC engine can run a compressor as needed. There can be several fiberglass-strengthened sausage-shaped air tanks placed around the chassis. Working out a brake energy regeneration system will be a bit complicated.
Keep in mind that big trucks all have dependable air compressors with dehydrator systems to avoid problems.

Posted by cfthelin

14th May 2012

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Speaking of "alternative vehicles"...

...I've noticed that SmartPlanet hasn't been keeping us up-to-date on Fisker. I wonder why.

Posted by JohnMcGrew@...

14th May 2012

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Why air?

Why use compressed air?

Liquid nitrogen is so much better - more expansive and more compressible, requiring smaller tanks.

Besides, the nitrogen would just be returning to the normal atmosphere, since it was taken out of the existing atmosphere, not manufactured.

Posted by joseph.vreeland@...

15th May 2012

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+2 Votes

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And where does one get inexpensive LN2?

Might as well use hydrogen. It's even more plentiful.

Posted by JohnMcGrew@...

16th May 2012

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